It's a great Bible study observation to see the balance placed in the Biblical text by the Spirit of God through these human authors. Immediately after contrasting the fearful approach to God through the law at Sinai (18-21) with the entrance into the grace of God through the "sprinkled blood" of the new covenant (24), our writer seems concerned his readers might come to the false conclusion it isn't quite as urgent to listen to God since we have been so lavishly embraced through lavishly gifted grace.
What could possibly go wrong now that our worst transgressions have been completely pardoned? Surely God's love isn't in short supply and His mercies are new every morning. We should be fine.
That's what makes the flow of ideas in this text so illuminating. Link up the last verse of last Sunday's text with the first verse of today's - Hebrews 12:24-25 - "[But you have come...] to Jesus, the mediator of a new covenant, and to the sprinkled blood that speaks a better word than the blood of Abel. See that you do not refuse him who is speaking. For if they did not escape when they refused him who warned them on earth, much less will we escape if we reject him who warns from heaven."
Forgive my repetition on a point here. There is much ink spilled these days telling the church the parts of the Old Testament citing God's wrath and judgment have no place in the New Testament's understanding of God. The fog has finally lifted. The mistakes of past misunderstandings of God have been corrected. Jesus has come and we now know God's true heart. He is always embracing, always loving, never wrathful, never judging.
But this doesn't seem to hold up. Far from cancelling out the revelations of divine wrath and judgment in the Old Testament, our writer endorses and builds on them. And he does it repeatedly in this New Testament letter.